Method of manufacturing an electronic device, and electronic device manufacturing apparatus

ABSTRACT

According to this disclosure, a method of manufacturing an electronic device is provided, which includes exposing a top surface of a first electrode of a first electronic component to organic acid, irradiating the top surface of the first electrode exposed to the organic acid with ultraviolet light, and bonding the first electrode and a second electrode of a second electronic component by heating and pressing the first electrode and the second electrode each other.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a division of U.S. patent application Ser. No.13/671,970, filed Nov. 8, 2012, which application is based upon andclaims the benefit of priority of Japanese Patent Application No.2012-009728, filed on Jan. 20, 2012, and Japanese Patent Application No.2012-149410, filed on Jul. 3, 2012, the entire contents of which areincorporated herein by reference.

FIELD

The embodiments discussed herein are related to an electronic device, amethod of manufacturing the electronic device, and an electronic devicemanufacturing apparatus.

BACKGROUND

Flip-chip mounting is one of the methods of mounting a semiconductorelement on a circuit board. In the flip-chip mounting, the circuit boardand the semiconductor element are electrically and mechanicallyconnected to each other by reflowing and connecting solder bumps formedon the surfaces of the circuit board and semiconductor element.

As the solder bumps are miniaturized, the distances between the adjacentsolder bumps get shorter. This can cause an electrical short circuitbetween the bumps which are melted by reflow. Moreover, as the solderbumps are reduced in diameter with the miniaturization, the density ofcurrent flowing through the solder bumps increases. This can notablycause electromigration in which the solder material flows along thecurrent.

To avoid such problems, instead of using the connection method usingsolder bumps, there is proposed a method in which the electrodes, suchas copper bumps, are bonded by performing thermocompression bonding onthe electrodes, thereby causing solid phase diffusion of the metalmaterials in the electrodes. This bonding method is also referred to assolid-phase diffusion bonding.

In the solid-phase diffusion bonding, unlike the connecting method usingsolder bumps, it is unnecessary to melt electrodes by reflow. Therefore,even when the distances between the adjacent electrodes are reduced, theelectrodes cannot be electrically short-circuited. The solid-phasediffusion bonding is therefore advantageous to miniaturization ofelectronic devices.

However, in the process of the solid-phase diffusion bonding, to promotediffusion of atoms between the electrodes, high temperature and highpressure are applied to semiconductor elements. This can damage thesemiconductor elements.

The technologies related to the following disclosure are disclosed inJapanese Patent Laid-open Publications No. 04-309474 and No. 05-131279.

SUMMARY

According to one aspect discussed herein, there is provided a method ofmanufacturing an electronic device, the method including exposing a topsurface of a first electrode of a first electronic component to organicacid, irradiating the top surface of the first electrode exposed to theorganic acid with ultraviolet light, and bonding the first electrode anda second electrode of a second electronic component by heating andpressing the first electrode and the second electrode each other.

According to another aspect discussed herein, there is provided anelectronic device including a first electronic component including afirst electrode, and a second electronic component including a secondelectrode bonded to the first electrode, wherein a crystal layer isformed between the first electrode and the second electrodes.

According to a still another aspect discussed herein, there is providedan electronic device manufacturing apparatus including a chamber, astage which is provided in the chamber and on which an electroniccomponent having an electrode is placed, and an ultraviolet lampprovided in the chamber and configured to irradiate the electrode withultraviolet light, wherein the ultraviolet lamp is provided at aposition where the ultraviolet lamp is capable of irradiating a topsurface of the electrode with the ultraviolet light

According to a yet another aspect discussed herein, there is provided anelectronic device manufacturing apparatus including a first chamber inwhich an oxidized film is removed from a surface of at least one of afirst electrode included in a first electronic component and a secondelectrode included in a second electronic component, a second chamberwhich is connected to the first chamber and in which at least one of thefirst electrode and the second electrode is irradiated with ultravioletlight, a bonder connected to the second chamber and configured to alignthe first electrode and the second electrode, and a third chamber whichis connected to the bonder and in which the first electronic componentand the second electronic component are heated and pressed against eachother.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claim.

It is to be understood that both the forgoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a process to bondelectronic components by solid-phase diffusion bonding;

FIGS. 2A to 2C are enlarged cross-sectional views in process of bondingfirst and second electrodes;

FIG. 3 is a configuration view of an electronic device manufacturingapparatus used in a first embodiment;

FIGS. 4A to 4K are cross sectional views of the electronic device inprocess of manufacture according to the first embodiment;

FIG. 5 is a cross-sectional view of an electronic device manufactured inthe first embodiment;

FIGS. 6A to 6D are cross-sectional views of an electronic device inprocess of manufacture according to a second embodiment;

FIG. 7 is a view for explaining experiment results in the secondembodiment;

FIG. 8 is a cross-sectional view of an electronic device manufacturingapparatus according to a third embodiment;

FIG. 9 is a plan view of an electronic device manufacturing apparatusaccording to a fourth embodiment;

FIG. 10 is a cross-sectional view of the electronic device manufacturingapparatus according to the fourth embodiment;

FIGS. 11A to 11G are cross-sectional views illustrating a method ofmanufacturing an electronic component according to the fourthembodiment;

FIG. 12 is a cross-sectional view of an electronic device manufacturingapparatus according to a fifth embodiment; and

FIGS. 13A to 13E are cross-sectional views of an electronic deviceaccording to a sixth embodiment.

DESCRIPTION OF EMBODIMENTS

Prior to the description of embodiments, preliminary matters aredescribed.

FIG. 1 is a cross-sectional view illustrating a process to bondelectronic components by solid-phase diffusion bonding.

In this example, the description is given of a case of bonding a firstelectronic component 30 and a second electronic component 40.

Among these electronic components, the first electronic component 30 isa circuit board. The first electronic component 30 includes firstelectrode pads 34 a and first passivation films 33 a, which are formedon a surface of a first silicon substrate 31.

On the first electrode pads 34 a, columnar first electrodes 35 a made ofcopper are formed by electroplating. The columnar electrodes are alsocalled bump electrodes or post electrodes.

On the other hand, the second electronic component 40 is a semiconductorelement. The second electronic component 40 includes second electrodepads 34 b and second passivation films 33 b, which are formed on asurface of a second silicon substrate 32. On the second electrode pads34 b, columnar second electrodes 35 b made of copper are formed byelectroplating.

The size of the second electrodes 35 b is not particularly limited. Inthis example, each second electrode 35 b has a shape of a square in aplan view, whose sides is about 10 μm.

Then, the first electrodes 35 a and second electrodes 35 b are alignedwith each other by an unillustrated flip-chip bonder in a state wherethe second electronic component 40 in a face down state is opposed tothe first electronic component 30.

To facilitate the alignment, it is preferable that the first electrodes35 a are larger than the second electrodes 35 b. In this example, eachfirst electrode 35 a has a shape of a square in a plan view whose sidesis about 15 μm.

FIGS. 2A to 2C are enlarged cross-sectional view illustrating the firstelectrode 35 a and the second electrode 35 b of FIG. 1 in a process ofbonding.

As illustrated in FIG. 2A, before bonding, each of the first and secondelectrodes 35 a and 35 b includes a plurality of copper crystal grains36. Then, the top surfaces of the first and second electrodes 35 a and35 b are flattened by CMP (chemical mechanical polishing) in advance soas to ensure the adhesion therebetween. By the CMP, the aforementionedcrystal grains 36 are exposed in the top surfaces of the first andsecond electrodes 35 a and 35 b.

Next, as illustrated in FIG. 2B, the first and second electrodes 35 aand 35 b are heated by the aforementioned flip-chip bonder while beingpressed against each other.

Here, when the heating temperature is low or the pressing load is smallin this process, the crystal grains 36 become discontinuous at theboundary between the first and second electrodes 35 a and 35 b, andthese electrodes 35 a and 35 b can be easily separated from each other.Accordingly, in order to merge the crystal grains 36 at the boundary, inthis process, the first and second electrodes 35 a and 35 b are heatedto a temperature higher than the recrystallization temperature of thecrystal grains 36 of copper and are also sufficiently pressed againsteach other with a load larger than 20 gf per bump.

By heating and pressing on the above conditions, the crystal grains 36around the boundary between the first and second electrodes 35 a and 35b are merged as illustrated in FIG. 2C, thus allowing the first andsecond electrodes 35 a and 35 b to be mechanically firmly connected.

However, by using this method, the first and second electroniccomponents 30 and 40 could be damaged by the high temperature of 300° C.and the load higher than 20 gf as described above.

Hereinbelow, a description is given of embodiments with reference to theaccompanying drawings.

First Embodiment

FIG. 3 is a configuration view of an electronic device manufacturingapparatus used in a first embodiment.

An electronic device manufacturing apparatus 20 according to the firstembodiment includes a first chamber 21, a second chamber 24, a flip-chipbonder 25, and a third chamber 26 and further includes transfer units 23a to 23 c therebetween.

The first chamber 21 is connected to an organic acid supply unit 22 andis supplied with gas containing organic acid. The first, second, andthird chambers 21, 24, and 26 are individually connected tounillustrated vacuum pumps and can be depressurized.

Between the first to third chambers 21, 24, and 26 and the respectivetransfer units 23 a to 23 c, unillustrated valves are provided to keepairtight in the first to third chambers 21, 24, and 26.

In the first embodiment, by using the electronic device manufacturingapparatus 20, the first and second electronic components 30 and 40,which are illustrated in FIG. 1, are electrically and mechanicallyconnected to each other in the following manner.

FIGS. 4A to 4K are cross-sectional views of the electronic device inprocess of manufacture according to the first embodiment.

As illustrated in FIG. 4A, the first and second electronic components 30and 40 are placed on a stage 21 c within the first chamber 21.

In the example described below, the first and second electroniccomponents 30 and 40 are chips diced from wafers. However, the followingprocess may be performed for wafers. Moreover, the following process maybe performed in a state where one of the first and second electroniccomponents 30 and 40 is a wafer and the other electronic component is achip diced from a wafer.

Then, in this state, while supplying the gas containing organic acidinto the first chamber from a gas inlet 21 a, extra gas within the firstchamber 21 is discharged out from a gas outlet 21 b.

The gas to be introduced into the first chamber 21 is generated at theorganic acid supply unit 22. The organic acid supply unit 22 includes atank 22 a charged with inert gas such as nitrogen, and a vessel 22 caccommodating liquid organic acid 22 b. The organic acid supply unit 22generates gas containing organic acid by bubbling the inert gas.

Although not particularly limited, formic acid is used as the organicacid in the present embodiment. Instead of formic acid, the organic acidmay be carboxylic acid such as acetic acid or oxalic acid.

As illustrated in FIG. 4B, just before being exposed to the organicacid, the top surface of the first electrode 35 a includes an oxidizedcopper film 1 with a thickness of 5 nm to 10 nm because copper isnaturally oxidized. Instead of the naturally oxidized film, a thermallyoxidized copper film may be formed as the oxidized film 1 to a thicknesslarger than the naturally oxidized film, for example, to a thickness ofabout 10 nm to 150 nm.

When the top surface of the first electrode 35 a with the oxidized film1 is exposed to formic acid, any one of the reactions expressed by thefollowing chemical formulas (1) and (2) proceeds depending on thecomposition of the oxidized film 1.CuO+2HCOOH→Cu(HCOO)₂+H₂O  (1)CuO₂+2HCOOH→Cu(HCOO)₂+H₂+O₂  (2)

By these reactions, as illustrated in FIG. 4C, an organic acid metalfilm 2 containing copper formate is formed on the top surface of thefirst electrode 35 a.

To advance the aforementioned reaction more quickly, it is preferablethat the first electrodes 35 a be heated to about 120° C. by anunillustrated heater incorporated in the first chamber 21.

In the first embodiment, as described later, an altered layer of copper,which includes an amorphous copper layer or a microcrystalline copperlayer, is formed from the organic acid metal film 2. Accordingly, inorder not to prevent formation of the altered layer of copper, it ispreferable that the heating temperature at this process is lower than130° C. which is a recrystallization temperature of amorphous ormicrocrystalline copper.

The pressure within the first chamber 21 is not particularly limitedtoo. However, when the oxidized film 1 is a naturally-oxidized film, theoxidized film 1 is thin and therefore can be entirely formed into theorganic acid metal film 2 even at reduced pressure. In the firstembodiment, the pressure within the first chamber 21 is set to a reducedpressure of about 600 mTorr, and the process is carried out for 30 min.

On the other hand, when the oxidized film 1 is a thermally-oxidized filmthicker than the naturally-oxidized film, entire oxidized film 1 can besurely formed into the organic acid metal film 2 by exposing theoxidized film 1 to formic acid at a pressure higher than atmosphericpressure.

Note that the organic acid metal film 2 is also formed on the topsurface of the second electrode 35 b (see FIG. 4A) by the same reactionas in the above.

Next, as illustrated in FIG. 4D, the first and second electroniccomponents 30 and 40 are transferred to the second chamber 24 using thetransfer unit 23 a (see FIG. 3).

As illustrated in FIG. 4D, the second chamber 24 includes ultravioletlamps 24 b and a stage 24 c. The first and second electronic components30 and 40 are placed on the stage 24 c with the electrodes 35 a and 35 bbeing face up.

Thus, the top surfaces of the first and second electrodes 35 a and 35 bare exposed to ultraviolet light generated by the ultraviolet lamps 24b.

The light sources of the ultraviolet lamps 24 b are not particularlylimited. However, in order to efficiently decompose copper formate inthe organic acid metal film 2, it is preferable that each ultravioletlamp 24 b is an excimer lamp with a wavelength shorter than wavelengthallowing decomposition of copper formate, for example, an excimer lampwith a wavelength of 172 nm. Note that the ultraviolet light with thiswavelength is also called vacuum ultraviolet (VUV) light.

The organic acid metal film 2 is irradiated with the aforementionedultraviolet light as illustrated in FIG. 4E. The organic acid metal film2 is therefore decomposed in accordance with the following chemicalformula (3).Cu(HCOO)₂→Cu+CO+CO₂+H₂  (3)

By this reaction, as illustrated in FIG. 4F, the altered layer 3 ofcopper, which contains non-crystalline amorphous or microcrystallinecopper, is formed in the top surface of the first electrode 35 a.

Irradiation time of the ultraviolet is not particularly limited. In thepresent embodiment, the irradiation time of the ultraviolet is about 5min to 15 min.

Furthermore, in order to promote the decomposition reaction by thechemical formula (3), it is preferable that the first electrodes 35 a beheated at a temperature ranging from about room temperature (20° C.) toabout 150° C.

The recrystallization temperature of the amorphous or microcrystallinealtered layer 3 is 130° C. Therefore, when this process is performed ata temperature higher than 130° C., the altered layer 3 isrecrystallized. Accordingly, it is preferable that the heatingtemperature of the first electrodes 35 a during the ultravioletirradiation is a temperature below 130° C. of the recrystallizationtemperature of amorphous or microcrystalline copper, for example, about120° C.

In the top surface of each second electrode 35 b, an altered layer 3 ofcopper is formed by the same processes as those illustrated in FIGS. 4Ato 4F.

Thereafter, as illustrated in FIG. 4G, the first and second electroniccomponents 30 and 40 are transferred to the flip-chip bonder 25 (seeFIG. 3). In the flip-chip bonder 25, the first and second electrodes 35a and 35 b are aligned with each other, and then the first and secondelectrodes 35 a and 35 b are heated to 100° C. and pressed with a loadof 5 gf to 10 gf per electrode for temporary bonding.

FIG. 4H is an enlarged cross-sectional view after this process iscompleted. As illustrated in FIG. 4H, just after the temporary bonding,the altered layers 3 of the first and second electrodes 35 a and 35 bare not merged with each other.

Preferably, the surfaces of the altered layers 3 of the first and secondelectrodes 35 a and 35 b are exposed to ultraviolet light before thetemporary bonding, so as to decompose and remove organic substances onthe surfaces of the altered layer 3 and thus cleaning the surfaces. Notethat the organic substances may be oxidized and removed by exposing thealtered layers 3 to oxygen plasma instead of ultraviolet light.

By removing the organic substances in such a manner, it is possible toprevent the bond strength between the first and second electrodes 35 aand 35 b from decreasing due to the organic substances.

To promote cleaning, the first and second electrodes 35 a and 35 b maybe heated to a temperature higher than the room temperature during theultraviolet or oxygen plasma irradiation. However, in order to preventrecrystallization of the altered layers 3, it is preferable that theupper limit of the temperatures of the first and second electrodes 35 aand 35 b at the heating is set lower than 130° C. of therecrystallization temperature of amorphous or microcrystalline copper inthe altered layers 3, for example, set to about 120° C.

Next, as illustrated in FIG. 4I, the first and second electroniccomponents 30 and 40 temporarily bonded to each other are transferredinto the third chamber 26.

As illustrated in FIG. 4I, the third chamber 26 includes a stage 26 c onwhich the first and second electronic components 30 and 40 are placed,and a press plate 26 b provided opposite to the stage 26 c.

A press unit 26 a is connected to the press plate 26 b. By the load fromthe press unit 26 a, the first and second electronic components 30 and40 located between the press plate 26 b and the stage 26 c are pressed.The pressing load is not particularly limited. However, in the firstembodiment, the pressing load is 10 gf per electrode, for example.

At the same time, the first and second electronic components 30 and 40are heated at a temperature of 150° C. to 250° C., which is higher thanthe recrystallization temperature of the altered layers 3, for about 10min to 30 min. This heating is performed by an unillustrated heaterincorporated in the stage 26 c.

FIG. 4J is a cross-sectional view of the first and second electrodes 35a and 35 b just after pressing is started in the aforementioned manner.

As illustrated in FIG. 4J, the altered layers 3 in the top surfaces ofthe first and second electrodes 35 a and 35 b are soft, and hence thealtered layers 3 can easily be deformed with a load less than that ofFIG. 1. Thus, the altered layers 3 come into close contact with no gap.

In particular, in the case where the oxidized films 1 (see FIG. 4B) arethermally-oxidized films, the altered layers 3 are thick enough and canbe easily deformed. This can implement better close contact between thefirst and second electrodes 35 a and 35 b.

Moreover, in this process, since the altered layers 3 are heated at atemperature higher than the recrystallization temperature of the alteredlayers 3, crystals of copper grow while the boundary portions of thealtered layers 3 are merged with each other.

As the result, as illustrated in FIG. 4K, the altered layers 3 turn intoa copper crystal layer 3 x, through which the first and secondelectrodes 35 a and 35 b are mechanically firmly bonded to each other.

Here, in the crystal layers 3 x formed by crystallizing amorphous ormicrocrystalline copper, the size of the copper crystalline grains issmaller than that of the first and second electrodes 35 a and 35 b. Inthe case of the present embodiment, the copper crystalline grains 36 inthe first and second electrodes 35 a and 35 b have an average diameterof about 5 μM, while the copper crystalline grains 3 y in the crystallayers 3 x have a smaller average diameter of about 1 μm to 3 μm.

Furthermore, in the interface between the first electrode 35 a and thecrystal layer 3 x, the orientations of the copper crystalline grains inthe electrode 35 a and layer 3 x become discontinuous in some cases.Such a state occurs also in the interface between the second electrode35 b and the crystal layer 3 x.

Note that the oxidized films in the surfaces of the first and secondelectrodes 35 a and 35 b may be removed in advance by exposing the topsurfaces of the first and second electrodes 35 a and 35 b to gascontaining organic acid such as formic acid before the first and secondelectrodes 35 a and 35 b are bonded in the aforementioned manner.

This can inhibit the formation of oxidized film in the bonding interfacebetween the first and second electrodes 35 a and 35 b, and thereforeprevent that the bonding of the first and second electrodes 35 a and 35b is inhibited due to the oxidized film.

Moreover, in order to further reduce the risk that the oxidized film isformed in the bonding interface, the first and second electrodes 35 aand 35 b may be bonded within the third chamber 26 that is configured tohave an atmosphere from which oxygen is excluded. Such an atmosphere is,for example, inert gas atmosphere or a vacuum atmosphere.

Note that the atmosphere within the third chamber 26 may be anatmosphere containing organic acid such as formic acid. The organic acidcan prevent formation of oxidized film in the bonding interface betweenthe first and second electrodes 35 a and 35 b.

The basic process of the method of manufacturing the electronic deviceaccording to the first embodiment is thus completed.

FIG. 5 is a cross-sectional view of an electronic device 59 manufacturedin the aforementioned manner.

According to the present embodiment, the first and second electrodes 35a and 35 b are bonded via the altered layers 3 of copper which has alower recrystallization temperature and is softer than crystallizedcopper. Accordingly, compared with the case of not forming the alteredlayers 3, the heating temperature and load applied to the first andsecond electrodes 35 a and 35 b can be reduced, and the first and secondelectrodes 35 a and 35 b can be bonded in a shorter time.

This can reduce thermal and mechanical damage received by the first andsecond electronic components 30 and 40 in the process of bonding thefirst and second electrodes 35 a and 35 b.

Moreover, since the first and second electrodes 35 a and 35 b can bebonded in a short time, it is possible to increase the throughput of theprocess of manufacturing the electronic devices and reduce the powerconsumption at manufacturing the same, thereby reducing theenvironmental burdens.

Moreover, the organic acid metal film 2 and altered layer 3 can beformed in a dry atmosphere. Accordingly, it is unnecessary to prepare awet-type manufacturing apparatus, and electronic devices can bemanufactured through a simple process.

Note that the first embodiment is not limited to the above description.For example, the altered layers 3 are formed in both of the first andsecond electrodes 35 a and 35 b in the above description. However, thealtered layers 3 may be formed only in the first electrodes 35 a or onlyin the second electrodes 35 b.

Furthermore, although the first electronic component 30 is a circuitboard and the second electronic component 40 is a semiconductor device,the electronic components to be bonded are not limited to thiscombination. For example, the first electronic components, which are thecircuit boards, may be bonded with each other. Alternatively, the secondelectronic components, which are the semiconductor elements, may bebonded with each other. This is also the case in the followingembodiments.

Furthermore, in the example of FIG. 3, all of the chambers 21, 24, and26 and the flip-chip bonder 25 are connected through the transfer units23 a to 23 c. However, all of the chambers 21, 24, and 26 and theflip-chip bonder 25 are not necessarily connected. For example, thefirst and second electronic components 30 and 40 may be exposed to anair after being temporarily bonded to each other in the flip-chip bonder24 and before being transferred to the third chamber 26. When theexposure time thereof does not exceed 10 hours, the bond strengthbetween the first and second electronic components 30 and 40 cannotdegrade, thereby avoiding the influence on the reliability of theelectronic components.

Second Embodiment

In the first embodiment, the oxidized film 1 (FIG. 4B) is used to formthe altered layer 3 (FIG. 4F) of amorphous or microcrystalline copper.

In a second embodiment, machining is used to thicken the altered layerthan in the first embodiment.

FIGS. 6A to 6D are cross-sectional views of an electronic device inprocess of manufacture according to the second embodiment. In FIGS. 6Ato 6D, the same elements as those described in the first embodiment aregiven the same reference numerals, and the description thereof isomitted below.

First, as illustrated in FIG. 6A, the surface of the first electrode 35a is cut by a diamond tool bit 70 to form an altered layer 73 ofamorphous or microcrystalline copper in the surface of the firstelectrode 35 a.

In this embodiment, the surface of the first electrode 35 a is cut underthe conditions where the diamond tool bit 70 rotates at acircumferential speed of 15 m/sec to 20 m/sec, for example, and thediamond tool bit 70 moves in the lateral direction of the substrateabout 20 μm per rotation.

Such machining disturbs copper crystals in the surface of the firstelectrode 35 a. Therefore, as illustrated in FIG. 6B, the altered layer73 of copper not having a crystalline structure is formed in a depthranging from 100 nm to 200 nm from the surface of the first electrode 35a.

Using the same method, the altered layer 73 of copper is formed in thesurface layer of the second electrode 35 b as illustrated in FIG. 6C.

Then, the processes of FIGS. 4A to 4F described in the first embodimentare performed to obtain the cross-sectional structure illustrated inFIG. 6D. As illustrated in FIG. 6D, in each of the first and secondelectrodes 35 a and 35 b, the altered layer 3, which is obtained fromthe organic acid metal film 2 by UV irradiation (see FIG. 4E), is formedon the altered layer 73 obtained by the aforementioned machining.

Thereafter, the processes of FIGS. 4I to 4K of the first embodiment areperformed to complete the basic structure of the electronic deviceillustrated in FIG. 5.

According to the present embodiment described above, by forming thealtered layer 73 of copper by machining, the altered layer 73 can beentirely made thicker than that of the first embodiment in which thealtered layer 3 of copper is formed from the oxidized film 1.Accordingly, the altered layers can deform more flexibly in the processof bonding the first and second electrodes 35 a and 35 b. Due to suchsoft altered layers 3 and 73, the first and second electrodes 35 a and35 b can come into close contact in a better manner.

Next, the experiment results of the present embodiment are described.

The experiment is performed to examine die shear strength of theelectronic device 59 manufactured in the present embodiment (see FIG.5). The die shear strength is defined as the maximum force that isapplied to the second electronic component 40 in the lateral directionof the substrate when the first and second electrodes 35 a and 35 b arepeeled from the interface between the first and second electrodes 35 aand 35 b.

The experiment results are illustrated in FIG. 7.

In FIG. 7, the horizontal axis indicates heating temperature of thefirst and second electrodes 35 a and 35 b in the process of FIG. 4J. Thevertical axis in FIG. 7 indicates the aforementioned die shear strength.

Graph A in FIG. 7 represents the experiment results obtained in thepresent embodiment. Graph B in FIG. 7 represents the experiment resultsin the case where only the machining illustrated in FIG. 6A is performedand the altered layer 3 derived from the oxidized film 1 of FIG. 6D isnot formed. Graph C in FIG. 7 represents the experiment results of acomparative example where the first and second electrodes 35 a and 35 bare directly bonded without performing machining (FIG. 6A) and withoutformation of the altered layers 3 (FIG. 6D).

The aforementioned die shear strength depends on the state of theinterfaces between the first and second electrodes 35 a and 35 b.

For example, in the Region I where the die shear strength is as small asabout 0 g/chip to 3000 g/chip, there are clear interfaces between thefirst and second electrodes 35 a and 35 b, and hence the bond strengthbetween the first and second electrodes 35 a and 35 b is low.

In the Region II where the die shear strength is 3000 g/chip to 7000g/chip, the interfaces between the electrodes disappear, and the firstand second electrodes 35 a and 35 b are substantially merged. However,in the Region II, the die shear strength is not high enough for theelectrodes to be considered completely merged. Thus, between theelectrodes, the previously described crystal layers 3 x are formed.

On the other hand, in the Region III where the die shear strength isabout 7000 g/chip to 12000 g/chip, the first and second electrodes 35 aand 35 b are substantially completely merged, and the crystal layers 3 xdo not exist therebetween.

As illustrated in FIG. 7, comparing the graphs at the same bondingtemperature, the die shear strength of Graph C of the comparativeexample is the smallest.

As for the Graph B with only machining, the die shear strength is higherthan that of the comparative example but is not high enough at a bondingtemperature of 175° C.

On the other hand, in the Graph A of the present embodiment, the dieshear strength at a bonding temperature of 175° C. is about twice asthat of the case of only machining.

Accordingly, it can be confirmed that the combination of machining andUV irradiation as in the present embodiment is effective on an increasein bond strength at a low bonding temperature of about 175° C. Since thebond strength is high enough at low bonding temperature of about 175° C.in this manner, the first and second electrodes 35 a and 35 b can bebonded without being heated to high temperature in the presentembodiment. Thus, the first and second electronic components 30 and 40are less likely to be damaged by heat.

Third Embodiment

In the first embodiment, as illustrated in FIG. 3, the first chamber 21for exposure to organic acid and the second chamber 24 for UVirradiation are used.

On the other hand, in a the present embodiment, a description is givenof an electronic device manufacturing apparatus in which the first andsecond electronic components 30 and 40 can be exposed to organic acidand ultraviolet light in a single chamber.

FIG. 8 is a cross-sectional view of the electronic device manufacturingapparatus according to the present embodiment.

As illustrated in FIG. 8, an electronic device manufacturing apparatus60 of the present embodiment includes a chamber 29 and a stage 29 faccommodated in the chamber 29. Above the stage 29 f, a window 29 c madeof heat-resistant glass is provided. The chamber 29 is partitioned bythis window 29 c into two compartments. Among these two compartments,the compartment above the window 29 c is used as an accommodationsection 29 b accommodating ultraviolet lamps 29 a.

On the other hand, the compartment below the window 29 c is providedwith a gas inlet 29 d, which is connected to the organic acid supplyunit 22, and a gas outlet 29 e. The stage 29 f includes an unillustratedheater and is capable of heating the first and second electroniccomponents 30 and 40 to a predetermined temperature.

In the electronic device manufacturing apparatus 60, each of the firstand second electronic components 30 and 40 are exposed to organic acid,such as formic acid, which is supplied through the gas inlet 29 d toform the organic acid metal film 2 (see FIG. 4C).

Furthermore, the organic acid metal film 2 is irradiated withultraviolet light from the ultraviolet lamps 29 a to form the alteredlayer 3 of amorphous or microcrystalline copper (see FIG. 4F).

In this manner, each of the first and second electronic components 30and 40 can be exposed to ultraviolet light and organic acid in thesingle chamber 29 in the present embodiment. Therefore, the apparatusconfiguration of the present embodiment can be made simpler than that ofthe first embodiment.

Furthermore, use of only the single chamber 29 in such a mannereliminates the need to transfer the first electronic component 30 andthe like from the first chamber 21 for exposure to organic acid to thesecond chamber 24 for ultraviolet irradiation like in the firstembodiment, and hence the transfer time can be reduced.

Moreover, the accommodation section 29 b is separated from the stage 29f by the window 29 c. This can eliminate the risk that radiation heatfrom the stage 29 f could damage the ultraviolet lamps 29 a.Accordingly, the temperature of the stage 29 f can be set higher than inthe case where the window 29 c is absent. Therefore, the first andsecond electronic components 30 and 40 can be irradiated withultraviolet light in a wide range of temperature.

Note that the stage 29 f may be provided with an unillustrated elevationmechanism so that the distance between the first electronic component 30and the ultraviolet lamps 29 a or between the second electroniccomponent 40 and the ultraviolet lamps 29 a can be adjustable. In thiscase, by adjusting the above distances so as to maximize the intensityof ultraviolet light irradiating the first and second electroniccomponents 30 and 40, the electronic components 30 and 40 can beefficiently irradiated with ultraviolet light.

Fourth Embodiment

In a fourth embodiment, the first and second electronic components 30and 40 are fixed to each other by a temporary bonding material in thefollowing manner.

FIG. 9 is a plan view of an electronic device manufacturing apparatusused in the fourth embodiment.

As illustrated in FIG. 9, an electronic device manufacturing apparatus50 of the present embodiment includes a first chamber 51 and a secondchamber 52.

Through the first and second chambers 51 and 52, a pair of transferrails 54 is inserted. On the transfer rails 54, a stage 55 movable inthe extending direction of the rails 54 is provided.

The first chamber 51 includes ultraviolet lamps 56 on the side surfacethereof and is connected to the organic acid supply unit 22.

Note that, on the side surface of each of the first and second chambers51 and 52, an unillustrated valve through which the stage 55 can go inand out is provided. The valves maintain the air tightness within thefirst and second chambers 51 and 52.

FIG. 10 is a cross-sectional view of the electronic device manufacturingapparatus illustrated in FIG. 9.

As illustrated in FIG. 10, the second chamber 52 includes a press plate58 and a press unit 57. The press unit 57 is expandable. The press plate58 moves up and down by the expansion movement of the press unit 57.

Between the first and second chambers 51 and 52, a connection unit 53 isprovided. The inside of the connection unit 53 is made airtight.Accordingly, the electronic components placed on the stage 55 can bemoved from the first chamber 51 to the second chamber 52 without beingexposed to the air.

Hereinafter, a description is given of the method of manufacturing anelectronic device using the manufacturing apparatus 50.

FIGS. 11A to 11G are cross-sectional views of an electronic deviceaccording to the present embodiment in process of manufacture. In FIGS.11A to 11G, the same elements as those described in the first embodimentare given the same reference numerals as those of the first embodiment,and the description thereof is omitted below.

First, after the first electronic component 30 is prepared asillustrated in FIG. 11A, a temporary bonding material 61 is attached tothe surface of the first electronic component 30 as illustrated in FIG.11B.

The material of the temporary bonding material 61 is not particularlylimited, but is preferably a material which volatilizes, melts, ordecomposes by heat to generate stickiness. Examples of such a materialinclude polyethylene glycol (PEG2000) with a molecular weight of about2000. Polyethylene glycol has a melting point of about 50° C. and is asolid at room temperature. However, when being heated to partially melt,polyethylene glycol can adhere to the first electronic component 30.

Moreover, instead of polyethylene glycol, the temporary bonding material61 may be any one of the group consisting of polypropylene glycol, butylcarbitol acetate, polyester, and polyhydroxy polyether. Alternatively,the temporary bonding material 61 may be a copolymer composed ofethylene and either one of polysulfonic acid and vinyl acetate.Moreover, the temporary bonding material 61 may be any one of the groupconsisting of acetic anhydride, succinic anhydride, and methyl acrylate,which volatilizes at a temperature of about 100° C. to 200° C.Furthermore, the temporary bonding material 61 may be methylmethacrylate or ethyl methacrylate which easily decomposes at atemperature of about 100° C.

In light of the productivity, it is preferable that the temporarybonding material 61 be applied before the first electronic component 30is cut out of a wafer by dicing.

Thereafter, as illustrated in FIG. 11C, an unillustrated flip-chipbonder is used to place the second electronic component 40 over thefirst electronic component 30, and the first and second electrodes 35 aand 35 b are aligned with each other.

Then, using heat from the flip-chip bonder, the second electroniccomponent 40 is heated at 120° C. for 15 sec, for example, to melt thetemporary bonding material 61. Thus, the first and second electroniccomponents 30 and 40 are temporarily bonded, while the gaps are madebetween the first and second electrodes 35 a and 35 b.

Next, as illustrated in FIG. 11D, the first and second electroniccomponents 30 and 40 are placed on the stage 55 and are transferred intothe first chamber 51.

Then gas containing organic acid such as formic acid is introduced intothe first chamber 51 through the gas inlet 51 a. The top surfaces of thefirst and second electrodes 35 a and 35 b are thus exposed to theorganic acid. Thus, the naturally-oxidized films and organic acid arereacted with each other in the surfaces of the first and secondelectrodes 35 a and 35 b to form the organic acid metal films 2 (seeFIG. 4C).

Next, the introduction of the gas containing the organic acid isstopped, and the gas in the chamber 51 is discharged from the gas outlet51 b.

Then, as illustrated in FIG. 11E, the top surfaces of the firstelectrodes 35 a and 35 b are irradiated with ultraviolet light generatedby the ultraviolet lamps 56 provided beside the first and secondelectrodes 35 a and 35 b, thus forming the altered layers 3 (see FIG.4F) of copper in the top surfaces of the first and second electrodes 35a and 35 b.

In the present embodiment, the ultraviolet lamps 56 are provided on theside surface of the first chamber 51 as described above. Accordingly,the ultraviolet light generated by the ultraviolet lamps 56 enters thegaps between the first and second electrodes 35 a and 35 b, and hencethe top surfaces of the first and second electrodes 35 a and 35 b can besurely irradiated with ultraviolet light.

Note that the stage 55 may include an unillustrated rotation mechanismand elevation mechanism and, by driving these mechanisms, the topsurfaces of the first and second electrodes 35 a and 35 b may evenly beirradiated with ultraviolet light.

Next, as illustrated in FIG. 11F, the stage 55 is moved along thetransfer rails 54 to move the first and second electronic components 30and 40 in the second chamber 52.

Then, the second electronic component 40 is pressed by the press plate58, while the first and second electrodes 35 a and 35 b are heated at atemperature lower than 130° C. which is the recrystallizationtemperature of the altered layers 3 (see FIG. 4H). Thus, the first andsecond electrodes 35 a and 35 b are temporarily bonded. Note that thisheating can be performed by an unillustrated heater incorporated in thepress plate 58 or stage 55.

Thereafter, while keeping the press plate 58 in the state of pressing,the heating temperature of the heater is increased to heat the first andsecond electronic components 30 and 40 to 170° C., thus polyethyleneglycol of the temporary bonding material 61 is volatized and removed.

As illustrated in FIG. 11G, while continuing the pressing by the pressplate 58, the first and second electronic components 30 and 40 areheated to 150 to 250° C. This state is held for about 30 min tocrystallize the altered layers 3 (see FIG. 4H), thereby bonding thefirst and second electrodes 35 a and 35 b. Thus, the electronic device59 illustrated in FIG. 5 is completed.

According to the present embodiment described above, while temporarybonding the first and second electronic components 30 and 40, the firstand second electronic components 30 and 40 are exposed to organic acidand ultraviolet light. Accordingly, the electronic devices can bemanufactured more efficiently than the case where the first and secondelectronic components 30 and 40 are individually subjected to theorganic acid and ultraviolet light.

Furthermore, since the inside of the connection unit 53 (see FIG. 10) ismaintained airtight, the copper altered layers 3 can be prevented frombeing exposed to the air on the way from the first chamber 51 to thesecond chamber 52. Therefore, it is possible to inhibit re-oxidizationof the altered layers 3, thereby preventing reduction in bond strengthbetween the first and second electrodes 35 a and 35 b due tooxidization.

Although the material volatilized by heat is used as the temporarybonding material 61 in the above, epoxy resin paste or epoxy resin filmmay be used as the temporary bonding material 61. In this case, thetemporary bonding material 61 does not volatilize by heat and can beleft as a part of underfill resin.

Fifth Embodiment

In the fourth embodiment, the first and second chambers 51 and 42 areused as illustrated in FIGS. 9 and 10. In contrast, in the presentembodiment, a description is given of an electronic device manufacturingapparatus in which the functions of these two chambers is unified.

FIG. 12 is a cross-sectional view of the electronic device manufacturingapparatus according to the present embodiment. In FIG. 12, the sameelements as those described in the fourth embodiment are given the samereference numerals as those of the fourth embodiment, and thedescription thereof is omitted.

A manufacturing apparatus 80 includes a chamber 53 provided with theultraviolet lamps 56, the press unit 57, and the press plate 58. Thechamber 53 is supplied with the gas containing organic acid such asformic acid from the organic acid supply unit 22 through a gas inlet 53a.

Furthermore, in the chamber 53, a stage 81 c, on which the firstelectronic component 30 is placed, is provided.

According to this, the plural of processes such as supply of organicacid, irradiation of ultraviolet light, and pressing of the secondelectronic component 40 against the first electronic component 30 can beperformed in the single manufacturing apparatus 80, and hence theapparatus configuration can be simplified.

Sixth Embodiment

In the first embodiment, the first and second electrodes 35 a and 35 bare made of copper. In the present embodiment, tin layers are formed onthe electrodes 35 a, 35 b in advance.

FIGS. 13A to 13E are cross-sectional views in process of manufacturingthe electronic device according to the sixth embodiment. In FIGS. 13A to13E, the same elements as those described in the first embodiment aregiven the same reference numerals as those of the first embodiment, andthe description thereof is omitted.

First, as illustrated in FIG. 13A, a low-melting point metal layer, suchas a tin layer 66, is formed on the top surface of each first electrode35 a by plating to a thickness of about 2 to 5 μm. When the tin layer 66is left in the air, an oxidized film 67 containing SnO or SnO2 is formedin the surface of the tin layer 66.

Next, as illustrated in FIG. 13B, the top surface of the tin layer 66 isexposed to organic acid. Here, formic acid is used as the organic acid.Then, an oxidized film 67 is reacted with the formic acid at atemperature of about 120° C. for about 30 min. Thus, the naturallyoxidized film 67 formed in the surface of the tin layer 66 reacts inaccordance with either chemical formula (4) or chemical formula (5) inthe following.SnO+2HCOOH→Sn(HCOO)₂+H₂O  (4)SnO₂+2HCOOH→Sn(HCOO)₂+H₂+O₂  (5)

By these reactions, an organic acid metal film 68 containing tin formateis formed on the top surface of the first electrode 35 a. Note that dueto the heating in this process, an intermetallic compound (Cu₆Sn₅) layer66 a made of tin and copper is formed in the interface between the firstelectrode 35 a made of copper and the tin layer 66.

Next, the surface of the organic acid metal film 68 is irradiated byultraviolet light. Thus, the organic acid metal film 68 is decomposed inaccordance with the following reaction formula (6).Sn(HCOO)₂→Sn+CO+CO₂+H₂  (6)

Tin produced by the above reaction forms an altered layer 69 ofamorphous or microcrystalline tin not having a crystalline structure asillustrated in FIG. 13C.

The similar process as the aforementioned process is also performed forthe second electrode 35 b, thereby forming the tin altered layer 69 inthe top surface of the second electrode 35 b.

Next, as illustrated in FIG. 13D, after the first and second electroniccomponents 30 and 40 are aligned by an unillustrated flip-chip bonder,the first and second electronic components 30 and 40 are heated andpressed against each other. Herein, the first and second electroniccomponents 30 and 40 are pressed and heated at a temperature of 150° C.for 5 min.

Accordingly, as illustrated in FIG. 13E, the altered layers 69 arecrystallized, and the tin layers 66 are merged with each other, thusbonding the first and second electrodes 35 a and 35 b to each other.Note that due to the heating in this process, the intermetallic compoundlayers 66 a grow thicker.

In such a manner, the basic structure of the electronic device 59illustrated in FIG. 5 is completed.

According to the present embodiment, the first and second electrodes 35a and 35 b are bonded via the altered layers 69 of tin, which is alow-melting point metal. Accordingly, the first and second electrodes 35a and 35 b can be bonded to each other in a shorter time at a lowertemperature than in the first embodiment using the altered layers 3 ofcopper (see FIG. 4J). This can further reduce damage on the first andsecond electronic components 30 and 40.

Note that the present embodiment is not limited to the above example.Although the tin layers 66 are formed on both the first and secondelectrodes 35 a and 35 b in the above, the tin layers 66 may be formedonly in the first electrodes 35 a or only in the second electrodes 35 b.

According to the above embodiments, the top surface of the firstelectrode exposed to the organic acid is irradiated with ultravioletlight to form the altered layer composed of an amorphous layer,microcrystalline layer, or the like. The first and second electrodes arethen bonded with the altered layer interposed therebetween. The alteredlayer has the lower recrystallization temperature and is softer than thecrystalline layer. It is therefore possible to reduce the temperatureand load applied in the process of bonding the first and secondembodiments, thus reducing damage on the first and second electroniccomponents.

All examples and conditional language provided herein are intended forthe pedagogical purpose of aiding the reader in understanding theinvention and the concepts contributed by the inventor to further theart, and are not to be construed as limitations to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although one or more embodiments of thepresent invention has been described in detail, it should be understoodthat the various changes, substitutions, and alterations could be madehereto without departing from the spirit and scope of the invention.

What is claimed is:
 1. A method of manufacturing an electronic device,the method comprising: exposing a top surface of a first electrode of afirst electronic component to a gas containing organic acid whileheating the first electrode; irradiating the top surface of the firstelectrode exposed to the gas containing organic acid with ultravioletlight; and bonding the first electrode and a second electrode of asecond electronic component by heating and pressing the first electrodeand the second electrode each other, and the method further comprising:thermally oxidizing the top surface of the first electrode, beforeexposing the top surface of the first electrode to the gas containingorganic acid.
 2. The method of manufacturing an electronic deviceaccording to claim 1, the method further comprising: exposing a topsurface of the second electrode to the gas containing organic acid; andirradiating the top surface of the second electrode exposed to the gascontaining organic acid with ultraviolet light.
 3. The method ofmanufacturing an electronic device according to claim 1, the methodfurther comprising: temporarily bonding the first electronic componentand the second electronic component with a temporary bonding material,before the bonding the first electrode and the second electrode.
 4. Themethod of manufacturing an electronic device according to claim 3,wherein the temporary bonding material is a material which isvolatilized, melted, or decomposed by heat in the bonding the firstelectrode and the second electrode.
 5. The method of manufacturing anelectronic device according to claim 1, wherein the bonding the firstelectrode and the second electrode is performed either in an atmospherefrom which oxygen is excluded or in an atmosphere containing organicacid.
 6. The method of manufacturing an electronic device according toclaim 1, the method further comprising: exposing at least one of the topsurfaces of the first electrode and the second electrode to ultravioletlight or oxygen plasma, before the bonding the first electrode and thesecond electrode.
 7. The method of manufacturing an electronic deviceaccording to claim 1, wherein in the bonding the first electrode and thesecond electrode, the first electrode and the second electrode areheated to a temperature higher than recrystallization temperature of analtered layer which is formed in the top surface of the first electrodeby the irradiation of the ultraviolet light.
 8. The method ofmanufacturing an electronic device according to claim 1, the methodfurther comprising: performing cutting on the top surface of the firstelectrode, before the exposing the top surface of the first electrode tothe gas containing organic acid.